Cyanobacteria (blue-green algae)

Bacteria and algae have been around since the beginning of life. Multiple characteristics distinguish cyanobacteria, also referred to as blue-green algae, from other organisms. At an age of 3.5 billion years, cyanobacteria are among the oldest known life forms. According to the University of California Museum of Paleontology, it is one of the most important bacteria on Earth.

For billions of years, the Earth’s atmosphere was incompatible with complex organisms. The environment was not only toxic, but it also lacked oxygen. Cyanobacteria are credited with helping create Earth’s oxygen-rich atmosphere. Blue-green algae are, in many respects, life-giving today, too. For example, the bacteria are a substantial nitrogen source for the fertilization of crops, including the food staples rice and beans. There is, however, a dichotomy: cyanobacteria are also a threat. Some strains produce toxins that pollute water, kill fish, and limit the sea’s bounty.

Background

Cyanobacteria have diversity within their family, but there is little variance in the microscopic form. Some variations occur in color; they are not always blue-green despite the name. The bacteria all contain chlorophyll and phycocyanin, which are responsible for photosynthesis. The phycocyanin provides the bluish pigment.

Water plants that can produce their own food by photosynthesis are algae. The usually single-celled organisms often form colonies that make them visible to the human eye. The bacteria contributed to plant evolution through an ancient endosymbiotic event in which a cyanobacterium took up residence within a eukaryote cell. The symbiotic relationship helped give rise to chloroplasts and plant photosynthesis through endosymbiosis.

A 2007 study in Australia reported evidence suggesting oxygen may have been present in parts of Earth’s oceans before the Great Oxidation Event. A more recent presentation by researchers at several universities supports the hypothesis of cyanobacteria providing the essentials for the change of the terrestrial habitat for complex life to flourish. Researchers have identified fossil thylakoid membranes in ancient cyanobacterial cells dating to about 1.75 billion years ago, providing additional evidence for the early evolution of oxygen-producing photosynthesis.

About 2.4 billion years ago, the Earth experienced a transition in its atmosphere that is known in scientific circles as the Great Oxidation Event. As the planet cooled down and life began in the shallow oceans, cyanobacteria were producing oxygen as a byproduct of their metabolism. Oxygen produced by cyanobacteria gradually accumulated in the atmosphere, leading to the Great Oxidation Event about 2.4 billion years ago.

Cyanobacteria have a significant history as a food source, especially in Asian countries. For example, spirulina is a cyanobacterium that is high in protein, easily cultivated in ponds, and used as a food supplement worldwide. It was a staple in Aztec and other ancient cultures as well. However, some forms of cyanobacteria, such as blue-green pond scum, have been responsible for poisoning fish, animals, and humans. Unless an individual is experienced in identifying the type of algae, it can be a lethal experience harvesting and consuming wild blue-green algae. Research has broadened the application of cyanobacteria in producing renewable chemicals, pharmaceuticals, and sustainable manufacturing processes.

Impact

The ability to provide a required nitrogen source for plants to grow is a two-edged sword for the environment. Too much nitrogen in the environment is also toxic. In fact, some studies have linked high nitrate exposure in drinking water to increased health risks, including certain cancers. We need the algae, but it requires management as well as education.

These algae can be found throughout the world, and most often in calm water that is nutrient-rich. Toxins from some cyanobacteria species, which impact humans and animals, can cause serious or even fatal consequences. The victims more often than not encounter the bacteria while drinking water or participating in recreational water activities. The effects of the toxins are dependent on the species of cyanobacteria. The symptoms may manifest as an allergic reaction, such as eye irritation, asthma, rashes, skin irritation, etc. Other ailments incurred can be stomach cramps, nausea, vomiting, diarrhea, sore throat, headache, fever, blisters of the mouth, liver damage, and muscle and joint pain. The toxins themselves are classified by the organ or system they impact. These would be liver (hepatotoxins), nervous system (neurotoxins), and others.

Though we know cyanobacteria are a worldwide health and environmental problem, comprehensive global statistics remain limited. Major efforts are underway through that organization to research and provide education to workers as well as consumers on best water practices. There are environmental concerns being addressed regarding wastewater and refuse being dumped untreated into the oceans, rivers, and streams in both developed and developing countries.

The Toledo, Ohio, area draws water from Lake Erie, where in 2014 a large toxic bloom of cyanobacteria impacted 500,000 residents. They were not the only people facing water problems from the bacteria’s toxins since it happens throughout the United States and the world. South Carolina has sustained a significant effect from the algae in its waterways and water systems. Clemson University cites several reasons: Lawn care and landscaping runoff are likely sources of eutrophication in stormwater ponds created along the coast. It occurs on farm ponds, streams, rivers, and reservoirs, plus more.

A problem with cyanobacteria blooms causing considerable angst is that it is hard to get rid of. While the bloom itself may be removed, it does not mean the level of the bacteria has been reduced.

An interesting cycle develops when it comes to nitrogen. Yes, the cyanobacteria are a source of it, frequently used to fertilize, as previously mentioned. It is also attracted to nitrogen. One of the most important prophylactic steps to inhibit the growth of the algae is the proper management of animal waste, which provides the conditions cyanobacteria need to flourish. These bacteria can grow in most moist, warm, lighted areas. They are not necessarily destroyed by heat. In fact, samples of a particular strain were identified in the hot springs of Yellowstone National Park. As global temperatures rise, management of the algae is of paramount importance.

Bibliography

“Architects of Earth’s Atmosphere.” UCMP Berkeley, n.d., www.ucmp.berkeley.edu/bacteria/cyanointro.html.

Bartram, J., and I. Chorus. “Water-Related Diseases.” Water Sanitation Health. World Health Organization, 2001, www.who.int/water_sanitation_health/diseases/cyanobacteria/en/.

“The Blue-Greens (Cyanobacteria).” Chebucto Community Net, 2 June 2016, lakes.chebucto.org/cyano. Accessed 1 June 2026.

Bryant, Donald. “Far-Red Light Makes Far-Reaching Algal Changes.” Joint Genome Institute. United States Department of Energy, 11 Sept. 2014, jgi.doe.gov/far-red-light-makes-far-reaching-algal-changes/. Accessed 1 June 2026.

“Cyanobacteria/Cyanotoxins.” U.S. Environmental Protection Agency, n.d., www2.epa.gov/nutrient-policy-data/cyanobacteriacyanotoxins.

Demoulin, C. F., et al. “Oldest Thylakoids in Fossil Cells Directly Evidence Oxygenic Photosynthesis.” Nature, vol. 625, 2024, pp. 529–34, doi:10.1038/s41586-023-06896-7. Accessed 1 June 2026.

“For Research on Cyanobacteria.” Cyanosite. Perdue U, n.d., www.cyanosite.bio.purdue.edu/. Accessed 1 June 2026.

Kendall, Brian. “Earth’s Oxygen Revolution.” WAT on Earth. U of Waterloo, Mar. 2014, uwaterloo.ca/wat-on-earth/news/earths-oxygen-revolution. Accessed 1 June 2026.

Khan, Ah, and C-S Phan. “Recent Advancement of Cyanobactins and Cyanobactin Prenyltransferases from 2021 to 2024.” Frontiers in Natural Products, vol. 4, 2025, article 1616031, doi:10.3389/fntpr.2025.1616031. Accessed 1 June 2026.

Schmelling, Nicolas M., and Moritz Bross. “What Is Holding Back Cyanobacterial Research and Applications? A Survey of the Cyanobacterial Research Community.” Nature Communications, vol. 15, no. 6758, 8 Aug. 2024, doi:10.1038/s41467-024-50828-6. Accessed 1 June 2026.

Wallover, Guinn Garrett. “Cyanobacteria: Understanding Blue-Green Algae’s Impact on Our Shared Waterways.” South Carolina Waterways. Clemson U Extension, Aug. 2015, www.clemson.edu/extension/hgic/water/resources_stormwater/cyanobacteria. Accessed 1 June 2026.

“A Whiff from Blue-Green Algae Likely Responsible for Earth’s Oxygen.” Phys.org. University of Waterloo, n.d., phys.org/news/2015-11-whiff-blue-green-algae-responsible-earth. Accessed 1 June 2026.